Surface-Active Characteristics

The surface-active properties of an inhibitor, in many instances, are inherent in the particular inhibitor molecule, but in some formulations are enhanced by the addition of other chemicals. Surface activity, in addition to influencing inhibitor effectiveness, determines dispersibility and detergency, which in turn affect the emulsion and foaming properties of the system. Detergency, the ability to clean a surface or keep a surface clean, is desirable because of the need for a clean surface onto which the corrosion inhibitor can be adsorbed. 

Foam or emulsion formation can seriously affect equipment operation and in a two-phase system can impede separation of the phases when it is necessary to do so. An example of the severe restriction placed on a corrosion inhibitor regarding foam or emulsion formation is that concerning the water tolerance of jet fuel. Water pick-up in the fuel must be limited, so that fuel lines will not freeze and plug during low-temperature operation. 

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Ledwidge, M. T. Corrigan, O. I., Effects of surface active characteristics and solid state forms on the pH solubility profiles of drug-salt systems, Int. J. Pharm. 174, 187-200 (1998). 

The surface activity characteristics of ll//-pyrido[2,l-6]quinazolin-ll-one and its 3-chloro, 2-methoxy, 8-methyl, and 2,4-dinitro derivatives were determined in 3% hydrochloric acid (85MI1). 

Surfactants are amphiphilic molecules widely used for different purposes in industrial processes, with a worldwide annual demand of about 10 billion (1,2). The most used surfactants are produced from petrochemical sources (3) however, compounds having surface activity characteristics may be synthetized by a wide variety of microorganisms (4,5). Such compounds, called biosurfactants, when compared with the syn-... 

A crude enzyme mixture was isolated from the fermentate of Candida rugosa (ATCC No. 14,830), which is reported to produce high activity lipases ( ). The enzyme mixture was added to a 20% butterfat emulsion. A cheese-like flavor developed after 3 hours of incubation at 37°C. A desirable Romano cheese note developed after continued incubation at room temperature for three days. Nelson (6) studied lipolyzed butterfat flavor and concluded that the surface active characteristics of both fatty acids and mono- and diglycerides were important in the lipolyzed system. A tempering period of hours or even days was usually required to establish equilibrium at the interface of aqueous and fat phases. He pointed out that the lipolyzed flavor appeared to intensify as the equilibration proceeded and that this intensification was sometimes mistaken for residual lipolytic activity. 

Furthermore, CS applications can be improved by synthesising some of its diverse derivatives. CS has an amino group, which allows the opportimity for N-alkylation, N-carboxylation, cyclisation and crosslinking (Figure 2.4). These derivatives possess good rheological and autoassociative and surface-active characteristics [20-23]. 

The poly(alkylene oxide)s are linear or branched-chain polymers that contain ether linkages in their main polymer chain structure and are derived from monomers that are vicinal cyclic oxides, or epoxides, of aliphatic olefins, principally ethylene and propylene and, to a much lesser extent, butylene. These polyethers are commercially produced over a range of molecular weights from a few hundred to several million for use as functional materials and as intermediates. Lower polymers are liquids, increasing in viscosity with molecular weight. The high polymers can be thermoplastic. Solubilities range from hydrophilic water-soluble polymers that are principally derived from ethylene oxide, to hydrophobic, oil-soluble polymers of propylene oxide and butylene oxide. A wide variety of copolymers is produced, both random copolymers and block copolymers. The latter may be used for their surface-active characteristics. 

The surface-active agents (surfactants) responsible for wetting, flotation and detergency exhibit rather special and interesting properties characteristic of what are called association colloids or, in the older literature, colloidal electrolytes. These properties play an important role in determining, at least indirectly, the detergency of a given surfactant and are therefore considered here... 

Perfluorinated carboxylic acids are corrosive liquids or solids. The acids are completely ionized in water. The acids are of commercial significance because of their unusual acid strength, chemical stabiUty, high surface activity, and salt solubiUty characteristics. The perfluoroaLkyl acids with six carbons or less are hquids the higher analogues are soHds (Table 1). 

Measurement of Surface Activity. Each surface-active property can be measured in a variety of ways and the method of choice depends on the characteristics of the substance to be tested. The most frequendy determined properties are surface tension (Y5q, Ylg) i t if cial tension (Yll> Tlg) contact angle (9), and CMC. 

Properties. Hydroxypropylcellulose [9004-64-2] (HPC) is a thermoplastic, nonionic cellulose ether that is soluble in water and in many organic solvents. HPC combines organic solvent solubiUty, thermoplasticity, and surface activity with the aqueous thickening and stabilising properties characteristic of other water-soluble ceUulosic polymers described herein. Like the methylceUuloses, HPC exhibits a low critical solution temperature in water. 

Weekman and Myers (W2) examined the fluid-flow characteristics of cocurrent downward flow of gas and liquid. The pulsing effect first noted by Larkins et al. was also observed in this work. Pressure-drop data could be correlated satisfactorily by a relation similar to those used for two-phase flow in pipes. Surface-active agents were observed to have a pronounced influence upon flow regime transition and pressure drop. 

The development of alkylbenzenesulfonates (ABSs) goes back to 1923, when the British chemist Adams discovered that it was possible to obtain water-soluble products by the sulfonation and neutralization of hexadecyl- and octadecyl-benzene. Such products have also soap-like characteristics [1]. In 1926 IG-Farbenindustrie (Hoechst) and Chemische Fabrik Pott, Pirna/Sachsen simultaneously discovered that long-chain ABSs have excellent surface-active properties. 

The curve shown in Fig. 6 for sodium dodecyl sulfate is characteristic of ionic surfactants, which present a discontinuous and sharp increase of solubility at a particular temperature [80]. This temperature is known as the Krafft temperature. The Krafft temperature is defined by ISO as the temperature [in practice, a narrow range of temperatures] at which the solubility of ionic surface active agents rises sharply. At this temperature the solubility becomes equal to the critical micelle concentration (cmc). The curve of solubility vs. temperature intersects with the curve of the CMC vs. temperature at the Krafft temperature. 

Exacting control of buffer preparation and the characteristics of capillaries and coatings is now recognized as key to successful electrophoretic separations.2 Repeatability of separations requires standardized surface preparation and rinse procedures. For example, capillaries can be coated with polyacrylamide using thionyl chloride surface activation. This approach was useful in DNA analysis.3 Non-aqueous buffers can be used to permit the use of thicker capillaries and higher voltages.4... 

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